As is well known, an intake manifold is connected to a cylinder head of an internal combustion engine (engine) for feeding intake air into combustion chambers of individual cylinders. The intake manifold is a considerably large-size component of the air-intake system, so for purposes of reducing the weight of the peripheral arrangement of the engine, the intake manifold is formed of synthetic resin instead of conventional light alloy (e.g., aluminum alloy and the like).
Since the intake manifold is an air-intake system component is exposed to lower temperature conditions than any air other-exhaust system component, it is feasible to form the intake manifold of synthetic resin (in particular, a synthetic resin of the type reinforced with fibers or the like). It is to be understood that the intake manifold is usually constructed in the form of a tubular member having plural outlet tube portions (equal in number to corresponding cylinders) branched from one inlet tube portion.
In the prior art, when manufacturing such an intake manifold from synthetic resin, separate halves in a pair, previously formed from synthetic resin, are brought in abutment against each other, and then joined together by applying an adhesive to their abutting surface or by thermally melting the abutting portions.
However, the intake manifold is subject to some degree of thermal effect and successive vibrations from the engine and the like, though temperature conditions are relatively low as compared with those in the exhaust system. Therefore, in order to stably ensure the reliability of the intake manifold for long-time use, it is necessary to use good care in the process of molding, with respect to various quality aspects, such as strength, rigidity, and sealing performance.
When aforesaid use conditions are considered, such prior art method as mentioned above can hardly be said to be sufficient to stably ensure high strength of bond between the separate halves and the sealing characteristics of the butt-joined portion. Further, for purposes of manufacturing a mass-production item such as intake manifold for mass-production automotive engines, a need exists for a method that can assure higher production efficiency.
As a method for molding a hollow tubular item, such as a synthetic resin-made pipe, it is known to bring synthetic resin-made halves into abutment against each other and fill a melted resin mass into an interior passage formed along peripheral edge of the abutting portions to thereby join the halves together to obtain a hollow molded product. It is also known to carry out such melted resin loading into the interior passage, within a molding die in which separate halves are molded when the separate halves are joined together as mentioned before.
By employing such a method, it is possible to more stably ensure high strength of bond between the so joined halves and good sealing performance of the buttjoined portion as compared to the prior art practice in which such joining is carried out by adhesion or thermal melting.
For example, in Japanese Patent Publication No. 2 -38377, there is disclosed a die construction including one pair of dies one of the dies has a male molding portion and a female molding portion for molding one separate half set and the other die has a female molding portion and a male molding portion provided in opposed relation to the molding portions of the one die. In this conjunction, there is also disclosed a method (called "die slide injection (DSI) method") where after separate halves are simultaneously molded (injection molded) by using such a pair of dies, one of the dies is caused to slide relative to the other die so that separate halves left in respective female molding portions are brought into abutment with each other, with melted resin being injected onto peripheral edges of the abutting portions to join the two halves together.
According to this DSI method, productivity can be considerably enhanced over the prior art method in which molding of separate halves and abutting/joining of the halves are carried out at separate stages.
An arrangement that can further enhance production efficiency is disclosed in, for example, Japanese Patent Publication No. 7-4830 that which teaches a rotary injection molding die construction. This die construction is basically a combination of molding dies adapted to be opened and closed relative to each other such that one of the molding dies is rotatable relative to the other die over a predetermined angular range, each die having a molding section consisting of at least one male molding portion and two female molding portions in a repetitive sequence of male/female/female in the direction of rotation for each rotational run over the predetermined angular range. In this conjunction, there is also disclosed a rotary injection molding method (so-called die rotary injection (DRI) method) wherein by using such a molding die assembly, molding separate halves and joining a pair of abutted halves are carried out during each rotational (e.g., forward-reverse) movement so that a finished product can be obtained for each rotational movement.
As is well known, an intake manifold is such that its inlet tube portion is connected to an air feed-side component, such as surge tank, while on the other hand its outlet tube portion is connected to an engine cylinder head. Further, for the convenience of layout within the engine room, the intake manifold is generally constructed in such a way that the inlet tube portion and the outlet tube portion are differently oriented, with their center lines extending at a predetermined angle (e.g., about right angle) to each other.
When molding a tubular member of such a configuration, it is commonplace for at least one of the inlet tube portion and outlet tube portion to be oriented in a direction different from the direction in which the molding die assembly is opened and closed as it is combined along a parting line. As such, molding operation is difficult with respect to the open end of aforesaid portion.
In particular, the DRI method involves not only opening and closing of the molding die assembly, but also relative rotation of the constituent dies of the assembly. This makes it more difficult to form a tube end portion oriented differently from the direction in which the die assembly is opened and closed.
The present invention is directed toward solving the foregoing problems, and accordingly it is a primary object of the invention to provide a method and apparatus for manufacturing a synthetic resin-made tubular member including differently oriented inlet tube portion and outlet tube portion which enable easy molding of a tube end portion oriented differently from the direction in which the molding die assembly is opened and closed, and a synthetic resin-made intake manifold having sufficient joint strength and sealing characteristics.